diff --git a/routers/README b/routers/README
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--- /dev/null
+++ b/routers/README
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+Redundant routers control
+==========================
+
+I'm using two Linux routers at home, along with a manageable switch and an ADSL
+modem.
+
+Both routers have their own address, and so does the switch. When one of the
+routers is active, it uses an additional address which serves as the default
+gateway for the rest of the boxes.
+
+One of the routers is an old box; it's rather slow, doesn't have much memory,
+and more importantly, it's dying. Obviously, it should only be used when the
+other one is down. However, if the connection has been established by that
+secondary router, the primary should not take over until the DSL link goes down
+on its own.
+
+The scripts in this directory are used to control which router is active.
+
+
+Checks on the primary router
+-----------------------------
+
+When the primary router is the active router:
+
+	1/ Check the switch
+	2/ If the switch is down, deactivate.
+
+When the primary router is inactive:
+
+	1/ Check the switch and the main router address
+	2/ If the switch is up and the main router does not exist, activate.
+
+
+Checks on the secondary router
+-------------------------------
+
+When the secondary router is the active router:
+
+	1/ Check the switch, the primary router, and a remote server
+	2/ If the remote server is reachable, do nothing
+	3/ If the switch is down, or if the primary router is up, deactivate.
+
+When the secondary router is inactive:
+
+	1/ Check the switch, the primary router, and the main router address
+	2/ If the switch is up, and both the primary router and the main router
+		address are down, activate.
+
+
+Installation
+-------------
+
+1/ Copy router-checks.conf to /etc, modify it however you want.
+
+2/ Copy share/ to /usr/local/share/router-checks (or to whatever you set the
+	LIB_DIR configuration variable to).
+
+3/ Modify activate.sh and deactivate.sh; they determine how a router becomes
+	the primary router and how a router releases primary routing control,
+	respectively.
+
+4/ Copy primary-router.sh or secondary-router.sh to
+	/usr/local/sbin/router-checks
+
+5/ If necessary (and if it will work on whatever distribution you use), use
+	the provided init script to start the checks on boot.
diff --git a/routers/init-script b/routers/init-script
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--- /dev/null
+++ b/routers/init-script
@@ -0,0 +1,67 @@
+#!/bin/sh
+#
+### BEGIN INIT INFO
+# Provides:          router-checks
+# Required-Start:    $local_fs networking
+# Required-Stop:     $local_fs networking
+# Should-Start:      iptables-persistent ip6tables-persistent
+# Should-Stop:       iptables-persistent ip6tables-persistent
+# Default-Start:     2 3 4 5
+# Default-Stop:      0 1 6
+# Short-Description: Router control
+### END INIT INFO
+
+. /lib/lsb/init-functions
+. /etc/router-checks.conf
+
+case "$1" in
+	start)
+		log_daemon_msg "Starting router control..." "router-checks"
+		if [ -f $PID_FILE ]; then
+			log_action_msg "PID file exists"
+			log_end_msg 1
+		fi
+		/usr/local/sbin/router-checks </dev/null >/dev/null 2>&1
+		sleep 1
+		if [ -f $PID_FILE ]; then
+			log_end_msg 0
+		else
+			log_end_msg 1
+		fi
+		;;
+
+	stop)
+		log_daemon_msg "Stopping router control..." "router-checks"
+		if ! [ -f $PID_FILE ]; then
+			log_action_msg "PID file not found"
+			log_end_msg 1
+		fi
+		rm -f $PID_FILE.`cat $PID_FILE`
+		sleep 2
+		if [ -f "$PID_FILE" ]; then
+			count=18
+			log_action_begin_msg " Waiting" 
+			while [ $count -gt 0 ] && [ -f "$PID_FILE" ]; do
+				sleep 5
+				log_action_cont_msg ""
+				count=$(( count - 1 ))
+			done
+			if [ -f "$PID_FILE" ]; then
+				log_end_msg 1
+			fi
+		fi
+		log_end_msg 0
+		;;
+
+	restart)
+		$0 stop
+		$0 start
+		;;
+
+	*)
+		echo "Usage: $0 {start|stop|restart|force-reload|status}" >&2
+		exit 1
+	;;
+esac
+
+exit 0
diff --git a/routers/primary-router.sh b/routers/primary-router.sh
new file mode 100644
index 0000000..ae5e9fd
--- /dev/null
+++ b/routers/primary-router.sh
@@ -0,0 +1,63 @@
+#!/bin/bash
+(
+
+. /etc/router-checks.conf
+
+exec >>$LOG_FILE 2>&1
+date
+echo "... STARTING"
+. "$LIB_DIR/pings"
+
+echo $$ > $PID_FILE
+stop_file="$PID_FILE.$$"
+trap "rm -f $stop_file" SIGINT SIGTERM
+touch $stop_file
+SLEEP_TIME=60
+while [ -f "$stop_file" ]; do
+	sleep $SLEEP_TIME
+	SLEEP_TIME=1
+
+	pr_switch=`mktemp`
+	if [ -f "$ACTIVATION_FILE" ]; then
+
+		# When the primary router is active, disable it if the switch
+		# is off-line
+
+		wait_pings `try_ping $SWITCH_ADDR $pr_switch`
+		if [ -f "$pr_switch" ]; then
+			date
+			echo "de-activating connection"
+			$LIB_DIR/deactivate.sh
+			rm -f "$ACTIVATION_FILE"
+			SLEEP_TIME=10
+		fi
+
+	else
+
+		# When the primary router is inactive, enable it if the switch
+		# is up and the main router IP does not exist
+
+		pr_main=`mktemp`
+		wait_pings `try_ping $SWITCH_ADDR $pr_switch` \
+			`try_ping $MAIN_ADDR $pr_main`
+		if [ -f "$pr_main" ] && ! [ -f "$pr_switch" ]; then
+			date
+			echo "activating connection"
+			$LIB_DIR/activate.sh
+			touch "$ACTIVATION_FILE"
+			SLEEP_TIME=20
+		fi
+		rm -f "$pr_main"
+
+	fi
+	rm -f "$pr_switch"
+done
+if [ -f "$ACTIVATION_FILE" ]; then
+	$LIB_DIR/deactivate.sh
+	rm -f "$ACTIVATION_FILE"
+fi
+date
+echo "... EXITING"
+rm "$PID_FILE"
+
+) &
diff --git a/routers/router-checks.conf b/routers/router-checks.conf
new file mode 100644
index 0000000..1783dfe
--- /dev/null
+++ b/routers/router-checks.conf
@@ -0,0 +1,25 @@
+# Router checks configuration
+
+# Some remote address to ping
+INTERNET_ADDR="173.194.34.1"
+
+# Main router address
+MAIN_ADDR="192.168.1.1"
+
+# Primary router's own address
+PRIMARY_ADDR="192.168.1.1"
+
+# Address of the switch
+SWITCH_ADDR="192.168.1.4"
+
+# PID files
+PID_FILE="/var/run/router-check"
+
+# Activation file, used to keep track of state
+ACTIVATION_FILE="/var/run/router-active"
+
+# Library directory - where scripts reside
+LIB_DIR="/usr/local/share/router-checks"
+
+# Log file
+LOG_FILE="/var/log/router-checks.log"
diff --git a/routers/secondary-router.sh b/routers/secondary-router.sh
new file mode 100644
index 0000000..8393fe4
--- /dev/null
+++ b/routers/secondary-router.sh
@@ -0,0 +1,73 @@
+#!/bin/bash
+(
+
+. /etc/router-checks.conf
+
+exec >>$LOG_FILE 2>&1
+date
+echo "... STARTING"
+. "$LIB_DIR/pings"
+
+echo $$ > $PID_FILE
+stop_file="$PID_FILE.$$"
+trap "rm -f $stop_file" SIGINT SIGTERM
+touch $stop_file
+SLEEP_TIME=60
+while [ -f "$stop_file" ]; do
+	sleep $SLEEP_TIME
+	SLEEP_TIME=1
+
+	pr_switch=`mktemp`
+	pr_peer=`mktemp`
+	if [ -f "$ACTIVATION_FILE" ]; then
+
+		# When the secondary router is active, disable it if the
+		# internet is not reachable and either the primary router is
+		# up or the switch is down
+
+		pr_internet=`mktemp`
+		wait_pings `try_ping $INTERNET_ADDR $pr_internet` \
+			`try_ping $PRIMARY_ADDR $pr_peer` \
+			`try_ping $SWITCH_ADDR $pr_switch`
+		if [ -f "$pr_internet" ]; then
+			if [ -f "$pr_switch" ] || ! [ -f "$pr_peer" ]; then
+				date
+				echo "de-activating connection"
+				$LIB_DIR/deactivate.sh
+				rm -f "$ACTIVATION_FILE"
+				SLEEP_TIME=10
+			fi
+		fi
+		rm -f "$pr_internet"
+
+	else
+
+		# When the secondary router is inactive, enable it if the
+		# switch is up and both the primary router and the main address
+		# are unreachable
+
+		pr_main=`mktemp`
+		wait_pings `try_ping $SWITCH_ADDR $pr_switch` \
+			`try_ping $PRIMARY_ADDR $pr_peer` \
+			`try_ping $MAIN_ADDR $pr_main`
+		if [ -f "$pr_main" ] && [ -f "$pr_peer" ] && ! [ -f "$pr_switch" ]; then
+			date
+			echo "activating connection"
+			$LIB_DIR/activate.sh
+			touch "$ACTIVATION_FILE"
+			SLEEP_TIME=20
+		fi
+		rm -f "$pr_main"
+
+	fi
+	rm -f  "$pr_peer" "$pr_switch"
+done
+if [ -f "$ACTIVATION_FILE" ]; then
+	$LIB_DIR/deactivate.sh
+	rm -f "$ACTIVATION_FILE"
+fi
+date
+echo "... EXITING"
+rm "$PID_FILE"
+
+) &
diff --git a/routers/share/activate.sh b/routers/share/activate.sh
new file mode 100644
index 0000000..e825098
--- /dev/null
+++ b/routers/share/activate.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+
+#
+# Example router activation script
+#
+# 1/ Remove default route through peer
+# 2/ Take active router address
+# 3/ Activate PPP link
+# 4/ Wait for a few seconds
+#
+
+ip route del default via 192.168.1.1 dev eth0
+ip addr add 192.168.1.1/24 dev eth0
+ifup ppp0
+sleep 10
diff --git a/routers/share/deactivate.sh b/routers/share/deactivate.sh
new file mode 100644
index 0000000..b2520f1
--- /dev/null
+++ b/routers/share/deactivate.sh
@@ -0,0 +1,18 @@
+#!/bin/bash
+
+#
+# Example router de-activation script
+#
+# 1/ Kill internet link
+# 2/ Nuke them from orbit, it's the only way to be sure
+# 3/ Release main router address
+# 4/ Add default route through peer
+#
+
+ifdown --force ppp0
+sleep 2
+killall -9 pppd
+sleep 2
+
+ip addr del 192.168.1.1 dev eth0
+ip route add default via 192.168.1.1 dev eth0
diff --git a/routers/share/pings b/routers/share/pings
new file mode 100644
index 0000000..b1f1aef
--- /dev/null
+++ b/routers/share/pings
@@ -0,0 +1,29 @@
+#!/bin/bash
+
+try_ping()
+{
+	export target="$1"
+	export prfile="$2"
+	export endfile=`mktemp`
+	(
+		if ping -c1 $target >/dev/null 2>&1; then
+			rm -f $prfile
+		fi
+		rm -f $endfile
+	) >/dev/null 2>&1 &
+	echo $endfile
+}
+
+wait_pings()
+{
+	local ok=0
+	while [ "$ok" = "0" ]; do
+		sleep 1
+		ok=1
+		for file in $*; do
+			if [ -f "$file" ]; then
+				ok=0
+			fi
+		done
+	done
+}